HOW CHARCOAL IS MADE 57 



The foul, bad-smelling gases which arise from sewers can 

 be prevented from escaping and passing to streets and build- 

 ings by placing charcoal niters at the sewer exits. Charcoal 

 is porous and absorbs foul gases, and thus keeps the region 

 surrounding sewers sweet, and clean and free of odor. Good 

 housekeepers drop small bits of charcoal into vases of flowers 

 to prevent discoloration of the water and the odor of decaying 

 stems. 



If impure water niters through charcoal, it emerges pure, 

 having left its impurities in the pores of the charcoal. Prac- 

 tically all household filters of drinking water are made of 

 charcoal. But such a device may be a source of disease in- 

 stead of a prevention of disease, unless the filter is regularly 

 cleaned or renewed. This is because the pores soon become 

 clogged with the impurities, and unless they are cleaned, the 

 water which flows through the filter passes through a bed of 

 impurities and becomes contaminated rather than purified. 

 Frequent cleansing or renewal of the filter removes this diffi- 

 culty. 



Commercially, charcoal is used on a large scale in the refin- 

 ing of sugars, sirups, and oils. Sugar, whether it comes 

 from the maple tree, or the sugar cane, or the beet, is dark 

 colored. It is whitened by passage through filters of finely 

 pulverized charcoal. Cider and vinegar are likewise cleared 

 by passage through charcoal. 



The value of carbon, in the form of charcoal, as a purifier 

 is very great, whether we consider it a deodorizer, as in the 

 case of the sewage, or a decolorizer, as in the case of the re- 

 fineries, or whether we consider the service it has rendered 

 man in the elimination of danger from drinking water. 



53. How Charcoal is Made. Charcoal may be made by 

 heating wood in an oven to which air does not have free 

 access. The absence of air prevents ordinary combustion, 



